Method for spreading sheets

ABSTRACT

A method for spreading thin soft rectangular articles such as cloths, unwoven cloths, paper sheets, plastic sheets, etc. (generally called &#34;rectangular sheets&#34;) is disclosed. A part of a first side of a rectangular sheet including one corner of a rectangular sheet is suspended in the air as held nearly horizontally by gripping the corner and another point on the side by grippers which are slidable on a horizontal rail. Accordingly, a second side of the rectangular sheet including the one corner is made to hang down nearly vertically. Then the lowermost end of the second side is gripped by another gripper that is movable vertically along a vertical rail. Except for the one corner, the initially held part of the one side is released, and the rectangular sheet is held with the two adjacent corners at the opposite ends of the second side gripped by two grippers which are movable on the rail. By separating these two grippers on the rail, the rectangular sheet can be spread out to be ready for the next processing step. If necessary, a part of the horizontal rail is tiltable so that the hanging second side can be held precisely vertically for facilitating the gripping of the lowermost end of the second side by the gripper on the vertical rail.

This application is a continuation of now abandoned application, Ser.No. 07/445,772 filed on Dec. 4, 1989, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for spreading thin softrectangular articles such as bed sheets, diapers, table cloths,handkerchieves, cloth wrappers, dress materials, all other cloths,unwoven cloths, paper sheets, plastic sheets or the like (hereinaftergenerally called "rectangular sheets" throughout the specification andclaims), and more particularly to a method for gripping corners ofrectangular sheets that is available in a spreading apparatus forrectangular sheets, a sorting apparatus for linens or other textilegoods, a spreading apparatus for linens or the like before laundry, andthe like.

2. Description of the Prior Art

Generally, in a laundry factory, arriving bed sheets, towels, covercloths and the like (hereinafter called "sheets") are washed as by acontinuous washing machine, and thereafter they are charged into adrying machine through a dewatering step, as shown in FIG. 16. Then,sheets having passed through a drying step are untangled and spreadedout, and after they have been subjected to ironing, they are folded andshipped. At this time, between the drying step and the ironing step,sheets taken out of a drying machine are conveyed to a predeterminedlocation by means of a belt conveyor, these sheets are picked andspreaded one by one from a block of sheets piled in heaps by a severalworkers, and then they are fed to an ironing apparatus or its auxiliaryapparatus (spreader, feeder or the like).

A spreading work for sheets having finished a drying step is heavilylaborious for workers under an unfavorable environment because it is awork within a high-temperature high-humidity atmosphere. Therefore,heretofore development of an apparatus for automating a spreading workfor sheets has been desired, but such an automated apparatus does notexist in the industry at present, and as a prior art, only afixed-position holding method for sheets was proposed in Japanese PatentPublication No. 59-24685 (1984).

This method consists of a first step of suspending a sheet while holdinga part thereof, a second step of holding the lowermost end of the sheetsuspended in the aforementioned first step and suspending the sheetwhile releasing the holding in the first step, a third step of holdingthe lowermost end of the sheet suspended in the second step, and afourth step of gripping the sheet at the two points held in theabove-mentioned second and third steps as stretched horizontally, andwith respect to a rectangular sheet the method will be explained in moredetail in the following.

If a rectangular sheet S is suspended while holding any arbitrary onepoint 027 thereon as shown in FIG. 17 in the first step, then a straightline passing through the held point 027 and a center of gravity 028 ofthe sheet S becomes vertical. Next, in the second step the sheet S issuspended while holding the lowermost point 029 under this condition andthe holding in the first step is released. As the third step, then thesheet S takes the attitude shown in FIG. 18, and the distance betweenthe top end 029 being held and the bottom end 030 of the sheet S becomesconstant. Hence in the third step, the bottom end 030 shown in FIG. 18is held. Next, in the fourth step if the top end 029 and the bottom end030 which are the held points in the second and third steps,respectively, are held horizontally, the sheet S takes the state shownin FIG. 19. Under this condition one may consider that the sheet S hasbeen held at fixed positions, and it could be transferred to the nextprocess. However, in order to hold the sheet S under an undoubledspreaded condition, in a fifth step one of the bottom ends 031 and 032in FIG. 19 is held and one of the previously held points 029 and 030 isreleased.

FIG. 20 is a schematic front view of a sheet fixed-position holdingapparatus that is available upon practicing the above-described methodfor holding a sheet at fixed positions, and for convenience ofexplanation the subject apparatus is severed into four sections A, B, Cand D. The construction of this sheet fixed-position holding apparatusis such that initial holding of a sheet and detection and holding of onecorner of the sheet are carried out in the section A, detection andholding of another corner diagonally opposite to the corner held in thesection A are carried out in the section B, in the sections B and C thesheet having its diagonally opposite two corners held is suspended withthe diagonal kept horizontal and further holding of only one of thecorners at the bottoms of the doubled sheet portion is carried out, andin the sections C and D adjacent two corners at the opposite ends of oneedge of the sheet are held at the same level, and thereby the sheet Scan be spreaded and held at fixed positions. In these figures, astroking rod 035 is provided in the proximity of a terminal end ofrightward movement of a chuck 033 so as to be movable vertically along aguide slot 036.

A chuck 037 is provided so as to be movable vertically along a guideslot 038 at a location under the terminal end of rightward movement ofthe chuck 033 and also to be movable from a lower dead point obliquelyin the right-upward direction along the same guide slot 038. Anotherstroking rod 039 is provided so as to be movable vertically along aguide slot 040 in the proximity of an upper dead point of the obliquemovement of the chuck 037. A chuck 041 is provided so as to be movableobliquely along a guide slot 042 with its lower dead point located underan upper dead point of the oblique movement of the chuck 037. A chuck043 is provided so as to be movable vertically along a guide slot 044 ata location under a middle point of the line connecting the upper deadpoints of the respective oblique movements of the chucks, 037 and 041,and also so as to be movable obliquely along the same guide slot 044with the uppermost point of the vertical movement placed at thelowermost point of the oblique movement. It is to be noted that thechucks 033, 037, 041 and 043 and the stroking rods 035 and 039 aredriven along the respective guide slots by air cylinders not shown.

In order to hold a rectangular sheet at fixed positions by means of theabove-described sheet fixed-position holding apparatus, the operation iscarried out in the following sequence.

At first, in the state shown in FIG. 21, a part of a sheet 045 to beheld at fixed positions is detected and held by the chuck 033, and thischuck 033 rises along a guide slot 034 then moves rightwards and becomesthe state shown in FIG. 22. In the state shown in FIG. 22, as thelowermost end of the sheet 045 suspended by the chuck 033 would notalways come right above the chuck 037, the sheet 045 is stroked by astroking rod 035 including a circular ring having a notch at one portionso that the lowermost end of the sheet 045 (a corner portion of thesheet 045) may come right above the chuck 037 which is positioned rightunder the chuck 033. Thereby, when the chuck 037 rises, it can hold oneof the corners of the rectangular sheet 045 at the lowermost end of thesheet as shown in FIG. 23. Thereafter the chuck 033 releases the sheet045. Also, the chuck 037 lowers and then rises in the right upperdirection along the guide slot 038. It is to be noted that at thismoment the stroking rod 035 returns to an upper dead point of a guideslot 036.

In the state shown in FIG. 24, the sheet 045 suspended by the chuck 037which has come to the upper dead point of the guide slot 038 anddirected downwards, is again stroked by a stroking rod 039, and sincethe lowermost end (the corner diagonally opposite to the corner held bythe chuck 037) of the sheet 045 comes to the position of a chuck 041 (afixed position determined depending upon the size of the sheet 045), theend is detected and held by the chuck 041. The chuck 041 holding thelowermost end of the sheet 045 rises up to an upper dead point along aguide slot 042, and so, as shown in FIG. 25 two diagonally opposedcorners of the sheet 045 are held at the same level (that is,horizontally). It is to be noted that at this moment the stroking rod039 returns to an upper dead point of a guide slot 040.

Next, in the state shown in FIG. 25, the sheet 045 having its onediagonal held horizontally with the corners at the opposite ends of thediagonal gripped by the chucks 037 and 041, has one of two hangingcorners gripped by a chuck 043 disposed at that position as opposed tothe chuck 041, while the chuck 037 is released, and by raising the chuck043 along a guide slot 044, the sheet 045 can be held at fixed positionsin a vertically elongated attitude. It is to be noted that in this sheetfixed position holding apparatus, since the distance between the upperright end position of the chuck 037 and the lower left end position ofthe chuck 041 is adjusted to be nearly equal to the length of thediagonal of the sheet to be treated, in the event that the chuck 037should have gripped two adjacent corners of the sheet 045 together inthe state shown in FIG. 23, the chuck 041 could not grip the sheet 045,and so it is compelled to again repeat the above-described holdingoperation for the sheet 045.

However, the sheet gripping mechanism used in the sheet fixed-positionholding apparatus in the prior art involved the following problems, Thatis, since the chucks 037, 041 and 043 are respectively disposed at fixedpositions, the apparatus could spread only a rectangular sheet ofpredetermined sizes, and it was practically not useful for sheets inwhich various sizes of sheets were mixed.

In addition, as shown in FIG. 25, in order to made the chuck 043 gripone corner of the sheet 045 while being spreaded from the section B tothe section C, it was essentially necessary to grip the sheet 045 withits diagonal stretched horizontally, and so, the entire apparatusnecessitated a broad space. Furthermore, as the chucks 037 and 041 gripthe lowermost ends of the sheet 045 always after the sheet was made tohang down in the direction of the gravity, at the gripped portions ofthe sheet, folds, creases, twists or the like would be necessarilygenerated, and in some cases they would adversely influenced uponfinishment by the subsequent ironing apparatus or the like.

SUMMARY OF THE INVENTION

It is therefore one object of the present invention to provide animproved method for spreading a rectangular sheet which is free from theaforementioned shortcomings of the known method in the prior art.

A more specific object of the present invention is to provide a methodand an apparatus for holding a rectangular sheet at fixed positions inpreparation for spreading the same sheet, which can deal withrectangular sheets having various sizes, which do not necessitate abroad space, and which do not generate folds, creases, twists or thelike at the gripped portions of the sheet and hence do not adverselyinfluence upon finishment by the subsequent processing.

According to one feature of the present invention, there is provided amethod for spreading a rectangular sheet, comprising the steps ofsuspending a part of a first edge including one corner of therectangular sheet in the air while holding the aforementioned partnearly horizontally to thereby make a second edge including theabove-mentioned one corner hang down nearly vertically, then holding thelowermost end of the second edge, thereafter releasing theaforementioned part of the first edge except for the above-mentioned onecorner, and thereby holding two adjacent corners at the opposite ends ofthe second edge of the rectangular sheet.

According to another feature of the present invention, there is provideda method for spreading a rectangular sheet, comprising the steps ofsuspending a part of a first edge including one corner of therectangular sheet in the air while holding the aforementioned partnearly horizontally, tilting the above-mentioned first edge by rotatingabout the above-mentioned one corner to thereby make a second edgeincluding the above-mentioned one corner hang down vertically, thenholding the lowermost end of the second edge, subsequently releasing apart or whole of the first edge, and thereby holding two adjacentcorners at the opposite ends of the second edge of the rectangularsheet.

According to still another feature of the present invention, there isprovided an apparatus for spreading a rectangular sheet, comprising atiltable rail for stretching and holding a part of a first edgeincluding one corner of the rectangular sheet nearly horizontally andtilting the aforementioned first edge by rotating about theabovementioned one corner to thereby make a second edge including theabove-mentioned one corner hang down nearly vertically, elevator meansincluding grippers which are vertically movable along the aforementionedsecond edge and adapted to grip the lowermost end of the second edgewhile moving up and down, and end detector means for detecting thelowermost end of the second edge.

In the case where the above-featured method and apparatus for holding arectangular sheet at fixed positions are employed in the process ofspreading rectangular sheets, rectangular sheets having various sizescan be dealt with without necessitating a broad space, moreover, folds,creases, twists or the like would not be produced at the grippedportions, and so, there is no fear that they would adversely influenceupon finishment by the subsequent ironing apparatus or the like.

The above-mentioned and other objects, features and advantages of thepresent invention will become more apparent by reference to thefollowing description of preferred embodiments of the invention taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic side view of a sheet spreading apparatus whichpractices a method according to a first preferred embodiment of thepresent invention;

FIGS. 2 to 8 are schematic views for explaining the successive steps inthe method for spreading a rectangular sheet according to the firstpreferred embodiment illustrated in FIG. 1;

FIG. 9 is a schematic side view of a sheet spreading apparatus whichpractices a method according to a second preferred embodiment of thepresent invention;

FIGS. 10(a), 10(b), 10(c) and 10(d) are perspective views showingsuccessive steps at a bed sheet charging station;

FIGS. 11(a), 11(b), 11(c), 11(d) and 11(e) are schematic views showingsuccessive steps at an essential section in the apparatus shown in FIG.9;

FIGS. 12, 13, 14 and 15 are schematic views showing successive steps inthe process of regripping a sheet as changing its direction by 90° inthe method according to the present invention;

FIG. 16 is a block diagram showing the successive steps for sheets fromarriving to shipping in a laundry factory in the prior art;

FIGS. 17, 18 and 19 are schematic views showing successive steps forexplaining a principle of a method for gripping a rectangular sheet atfixed positions in the prior art;

FIG. 20 is a schematic side view of a sheet spreading apparatus in theprior art; and

FIGS. 21, 22, 23, 24 and 25 are schematic partial side views of the sameapparatus in the prior art showing successive steps in the process ofgripping a rectangular sheet at fixed positions.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

Now a first preferred embodiment of the present invention will bedescribedwith reference to FIGS. 1 to 8. In these figures, referencenumerals 1 and 2 designate sheet edge grippers such as those disclosedin, for instance, Laid-Open Japanese Utility Model Specification No.63-90614 (1988), they are grippers mounted to an indexing-drive conveyor3 and adapted to grip apart of a shorter edge ac of a rectangular sheet4 including one corner a thereon as actuated by an operator. It is alsopossible to automate the gripping of the sheet edge. The conveyor 3 hasthe edge grippers 1 and 2 and the like mounted thereto at a desiredpitch, it is driven in the direction of arrows as indicated in thefigure, it can stop at a predetermined stop position, and also it canperform an indexing operation.

Reference numerals 4-7 designate rectangular soft sheets. It is to benotedthat while the sheets 4-7 are identical, in order to facilitate tounderstand the respective steps they are differentiated by differentreference numerals. Reference numerals 8-13 designate corner grippers,which are movable along a vertical rail 14, rails 17 and 19, andconveyor rails 15 and 18 while gripping the corners (a and b, or a andc) of the sheets 4-7. These corner grippers 8-13 could be any known onessuch as thesheet conveying chucks proposed in Laid-Open Japanese UtilityModel Specification No. 63-104310 (1988). The vertical rail 14 is aguide rail for moving a corner gripper 8 up and down along a hanginglonger edge of asheet 5. The above-mentioned rails 17 and 19 are suchrails that the cornergrippers 8-13 can move thereon by rolling due totheir own gravities. Reference numeral 16 designates a feeding device,which is a device for stretching and spreading a sheet 6 carried in asgripped by corner grippers 10 and 11 into the state of a sheet 7 bybroadening an interval between corner grippers 12 and 13, and thenfeeding the sheet 7 to a roll type ironing apparatus in the subsequentstep. This apparatus could be a known apparatus in the prior art asdisclosed in Japanese Patent Publication No. 58-22240 (1983).

Reference numeral 20 designates an elevator bracket which is moved upand down along the vertical rail 14 by means of an elevator device 24consisting of a ball screw and a nut or the like, at the tip end of thebracket 20 is mounted a corner detector 21 consisting of aphoto-electric sensor for detecting the lowermost end of the sheet 5,and further is mounted a known opener 23 (for instance, Laid-OpenJapanese Utility Model Specification No. 63-104310 (1988)) for openingand closing the corner gripper 8. As the opener 23, a device disclosedin the above-referred laid-open U.M. specification can be utilized. Theelevator bracket 20 moves up and down along the vertical rail 14 whilesupporting the movable gripper 8, and at the position where thelowermost end of the hanging sheet 5 has been detected by the cornerdetector 21, it makes the gripper 8 grip the hanging sheet 5. Thedetector 21 is a sensor such as a photo-electric sensor, a limit switchor the like which can detected the lowermost end of the sheet. Referencenumeral 22 designates an opener fixed in position to the rail 14 formaking the corner gripper 9 grip the upper corner of the sheet 5.

Now description will be made on the operation of the first preferredembodiment of the present invention constructed in the above-describedmanner. At first, the operation will be explained with respect to thecasewhere a rectangular sheet 7 is spreaded with its longer edge abplaced at the upper edge as shown in FIG. 5.

1 An operator makes an edge gripper 1 grip an edge portion L of arectangular sheet 4 which portion is a part of one shorter edgeincluding one corner a as shown in FIG. 2. In this case, the edgeportion L could begripped by one edge gripper after having beenstretched straightly, or elsea point a and a point x at the oppositeends of the edge portion L could begripped separately by two grippersand held after being spreaded in the next step (FIG. 3).

2 The edge portion L gripped in Step 1 above is held horizontally in theair as shown in FIG. 4. In this case, the edge portion L could be heldas stretched and spreaded by two grippers in the air as described above.If arectangular sheet is held in the air in the above-described manner,then asshown in FIG. 4, the side of a longer edge 5a of the rectangularsheet 5 including the one corner a would necessarily hang down nearlyvertically under the one corner a due to the gravity. Accordingly,regardless of the size of the sheet, a corner b adjacent to the onecorner a on the longer edge would be always positioned at the lowermostend of the sheet 5 along the hanging longer edge 5a nearly right underthe one corner a.

3 If the gripper 8 moves up and down along the hanging longer edge 5aunderthe one corner a, then it can detect and grip the corner b which isthe lowermost end of the sheet 5.

4 Subsequently, in the case where the edge portion L is held gripped byoneedge gripper, only the one corner a is regripped by the gripper 9 andthe edge portion L is released. Otherwise, in the case where the point aand the point x at the opposite ends of the edge portion L are heldgripped byseparate grippers, only the point x is released and the pointa is regripped by the gripper 9. Then the state where only the point aand the point b are gripped by the grippers 9 and 8, respectively, isrealized, and so, if these two points are separated horizontally in theair, then asshown in FIG. 5, the rectangular sheet 7 can be stretchedand spreaded withits longer edge ab placed at the upper edge.

5 As described above, if the point a and the point b are gripped by thegrippers 9 and 8, respectively, since the sheet 7 can be gripped under astretched and spreaded condition, pretty and precise gripping wouldbecomepossible in distinction from the gripping under a folded, creasedor twisted condition of corners in the prior art.

Next, the operation will be explained with respect to the case where arectangular sheet is spreaded with its shorter edge ac placed at theupperedge as shown in FIG. 8.

6 An edge portion H of a rectangular sheet 4 which portion is a part ofonelonger edge including one corner a is gripped by an edge gripper 1.In thiscase, the edge portion H could be gripped by one edge gripperafter having been stretched straightly, or else a point a and a point yat the oppositeends of the edge portion H could be gripped separately bytwo grippers and held after being spreaded in the next step (FIG. 6).

7 The edge portion H gripped in Step 6 above is held horizontally in theair as shown in FIG. 7. In this case, the edge portion H could be heldas stretched and spreaded by two grippers in the air as described above.If arectangular sheet is held in the air in the above-described manner,then asshown in FIG. 7, the side of a shorter edge 5b of the rectangularsheet 5 including the one corner a would necessarily hang down nearlyvertically under the one corner a due to the gravity. Accordingly,regardless of the size of the sheet, a corner c adjacent to the onecorner a on the shorter edge would be always positioned at the lowermostend of the sheet 5 along the hanging shorter edge 5b nearly right underthe one corner a.

8 If the gripper 8 moves up and down along the hanging shorter edge 5bunder the one corner a, then it can detect and grip the corner c whichis the lowermost end of the sheet 5.

9 Subsequently, in the case where the edge portion H is held gripped byoneedge gripper, only the one corner a is regripped by the gripper 9 andthe edge portion H is released. Otherwise, in the case where the point aand the point y at the opposite ends of the edge portion H are heldgripped byseparate grippers, only the point y is released and the pointa is regripped by the gripper 9. Then the state where only the point aand the point c are gripped by the grippers 9 and 8, respectively, isrealized, and so, if these two points are separated horizontally in theair, then asshown in FIG. 8 the rectangular sheet 7 can be stretched andspreaded with its shorter edge ac placed at the upper edge.

○ 10 Therefore, the same advantage over the method in the prior artasdescribed in Section 5 above can be obtained.

Next, a second preferred embodiment of the present invention will bedescribed with reference to FIGS. 9 to 15.

In these figures, reference numeral 101 designates a sheet grippingdevice such as, for instance, the device disclosed in Laid-Open JapaneseUtility Model Specification No. 63-90614 (1988). Grippers 102, 103,102', 103', . . . moving along a rail 109 are successively fed to thesheet gripping device 101. Among these grippers, grippers 102' and 103'arriving at the illustrated positions are opened by means of aircylinders not shown, and when an operator 115 inserts a corner portionof one sheet 104' on a conveyor 111 for conveying sheets 104" into theseopened grippers 102' and103' (into a sheet charging port), the grippers102' and 103' would automatically grip the sheet 104'. Under thiscondition, if the sheet gripping device 101 is rotated by 90° in thehorizontal plane, thenthe state of gripping a sheet 104 by grippers 102and 103 as shown in FIG. 10(b) is realized, and at this moment, otherempty grippers are fed to thesame position (the position of the grippers102' and 103' in FIG. 9) and opened in a similar manner. In addition,reference numerals 122 and 123 inFIG. 11 designate grippers for grippingend portions of a vertical side edge. On the other hand, theabove-mentioned sheet 104' is a sheet having a portion close to onecorner gripped by the grippers 102' and 103', whilesheets 104 and 107are sheets gripped by grippers 102 and 103 at the positions separated byabout 50 cm from each other, a sheet 110 is a sheethaving a part of itsedge A suspended nearly horizontally, and a sheet 141 is a sheet grippedby grippers 132 and 133, respectively, at the positionsclose to theopposite ends of one edge.

Reference numeral 105 designates a stroking rod, which is a rod used forstroking a sheet 104 when the sheet 104 fed to a sheet charging port(FIG.10(a)) was rotated by 90° by the sheet gripping device 101 (FIG.101(b)) and then the gripper 102 is raised upwards by about 50 cm bymeans of an air cylinder not shown (FIG. 10(c)). At this time thegripper 103 opensto guide the sheet 104, and thereafter it closes togrip the sheet 104. Reference numerals 106 and 129 designate driverails, which are rails associated with drive units for raising thegrippers 102, 103, 122 and 123as disclosed, for instance, in Laid-OpenJapanese Utility Model Specification No. 63-90614 (1988). In addition,reference numeral 108 designates a corner revealing device which servesto untangle a corner portion of a suspended sheet 107, and it is adaptedto reveal a corner of a sheet by beating an edge of the sheet.

Reference numeral 121 designates a tiltable rail, which is a railcapable of being subjected to tilting motion about a fulcrum pin 120 bymeans of an air cylinder 125 (FIG. 11(b)) as shown in FIG. 11. Referencenumeral 124 designates another rail contiguous to the tiltable rail 121,which accepts a gripper 102 gripping one corner of a sheet 110 (FIG.11(b)) and fixes the position of the gripper 102 by means of a stoppernot shown. Reference numeral 126 designates a gripper feeder whichaccepts grippers 112 and 113 being fed from a rail 143 into the feederand after they have been rotated by 180° means of an indexing device127, these grippers 112 and 113 are fed into the vertical rail 128. Thisdevice is similar to that disclosed, for example, in Laid-Open JapaneseUtility Model Specification No. 63-139864 (1988). Reference numeral 145designatesan elevator device which involves a drive unit for moving anelevator bracket 130 up and down.

Reference numeral 130 designates an elevator bracket, which is moved upanddown along a vertical rail 128 by the elevator device 145, and to thetip end of the elevator bracket 145 is mounted a corner detector device131 such as a photo-electric sensor or the like for detecting thelowermost end of the sheet 110. In addition, an opener 135 for openingand closing acorner gripper 122 such as disclosed, for instance, inLaid-Open Japanese Utility Model Specification No. 63-104310 (1988), isalso mounted to the bracket 130. The elevator bracket 130 moves up anddown while supporting the corner gripper 122 which is movable along thevertical rail 128, and at the position where the lowermost end of thehanged sheet 110 has been detected by the corner detector device 131,the elevator bracket 130 makesthe gripper 122 grip the lowermost end ofthe sheet 110. Reference numeral 134 designates an edge detector device(FIGS. 11(b) and 11(c)), which is adevice for detecting the fact that anedge B of the sheet 110 has been hanged vertically when the tiltablerail 121 is tilted, and normally a photo-electric tube is used for thisdevice. In addition, reference numeral 142 in FIG. 9 designates a sheetfeeder which makes grippers 132 and 133 move to the left and to theright, and thereafter feeds a sheet tothe subsequent step under aspreaded condition by releasing the gripping.

Next, the operation of the above-described apparatus will be explainedwithreference to FIGS. 9 to 15. At first, as shown in FIG. 9, anoperator 115 picks up one of the sheets 104" on the conveyor 111, andinserts a point aat the end of one edge (FIG. 12) into a sheet chargingport (FIG. 10(a)). Grippers 102' and 103' have been preliminarily fed tothe sheet charging port and opened, and when the feed of one sheet 104'has been detected as by a photo-electric tube or the like not shown,they are automatically closed. In response to a signal representing theclosure of the grippers, the sheet gripping device 101 rotates by 90°(FIG. 10(b)), then while a gripper 102 is held gripping the sheet 104,the other gripper 103 is opened by an air cylinder not shown, and fixedin position. Under this condition, the gripper 102 is pushed up by about50 cm by means of anotherair cylinder not shown (FIG. 10(c)), and thegripper 103 is closed. Throughthese operations, the gripper 103 canautomatically grip a point x of the sheet 110 shown in FIG. 13. It is tobe noted that the distance between the point a and the point x isproperly selected to be 50 cm±20 cm.

At this time, a stroking rod 105 is pushed out so as to perform theaction of stroking the sheet 104, so that the sheet 104 would notdisengage from the gripper 103 and the sheet 104 can be grippedprecisely at the point x.Thereafter, the stroking rod 105 is returned toits original position, and the sheet gripping device 101 becomes readyto accept the next succeeding sheet 104 (FIG. 10(d)). A sheet 107 havingits point a and point x grippedby the grippers 102 and 103 is raised bythe drive rail 106 and is conveyedwhile being hanged in the air. In themidst of this conveyance is provided a corner revealing device 108. Thesheet 107 is beated by this corner revealing device 108 and therebyuntangled, and so a point b at the cornerportion can be revealed underthe gripper 102. The sheet 110 having its corner point b revealed isconveyed as gripped by the grippers 102 and 103, and these grippers 102and 103 are conveyed onto the tiltable rail 121.

Here, if the point a and the point x are held horizontally, that is, atthesame level as shown in FIG. 13, then since the center of gravity ofthe sheet 110 is located at a position deviated from the gripped pointsa and x, the corner point b would be at a position displacedhorizontally by l cm from the top of the right edge of the sheet 110 asshown in FIG. 13. This distance of displacement is about 40 cm at themaximum in the case where the shorter edge A of the sheet 110 is 2 m andthe longer edge A thereof is 3 m, and this will vary depending uponsizes, a residual moisture proportion, gripping positions at the point aand the point x, and the like of the sheet.

Accordingly, in order to grip precisely the end point b of the side edgeB,the gripper 102 conveyed onto the tiltable rail 102 is further sentonto the rail 124 and fixed in position as shown in FIG. 11(b).Subsequently, an air cylinder not shown is made to act so that the edgeportion of the sheet 110 between the gripped points a and x may bestretched on the tiltable rail 121, and also the tiltable rail 121 ismade to tilt about a pin 120 at the fulcrum point (FIG. 11(c)). The tiltangle is controlled bymeans of the edge detector device 134.

After the side edge B has hanged nearly vertically, the elevator bracket130 descends along the vertical rail 128. The descended elevator bracket130 stands by jointly with the gripper 122 at the position where thepointb on the side edge B of the sheet 110 can be gripped. The elevatorbracket 130 descends by a distance corresponding to the length of theside edge B of the sheet 110, and so, even a sheet having a differentlength can be gripped by the gripper 122 precisely at the corner point b(FIG. 11(d)). Thereafter, the rail 124, and the grippers 102 and 103 onthe tiltable rail 121 are released by actions of air cylinders notshown, and the sheet110 descends along the vertical rail 128 as grippedby the grippers 122 and123 at the point a and the point b.

The descended grippers 122 and 123 (FIG. 11(e)) are raised by the driverail 129, and fed to the sheet feeder 142 as shown in FIG. 9. Thegrippers122 and 123 are automatically separated to the left and theright, their gripping is released, and the sheet is fed to a roll ironeror the like inthe subsequent step under a spreaded condition. It is tobe noted that the method of spreading a sheet according to the presentinvention is applicable to either a rectangular sheet or a square sheet.In addition, it is also becomes possible by changing the arrangement ofrails that the gripper 102 is continuously used in place of the gripper123 and the opposite end portions of the side edge B are gripped by thegrippers 102 and 122. While the preferred embodiments were explainedabove in connection to rectangular sheet, even in the case of a squaresheet, gripping of corners can be achieved in the similar manner.

As described in detail above, since the present invention ischaracterized by a number of novel features, according to the presentinvention even a bag-shaped sheet (a blanket cover or the like),spreading of the sheet is possible provided that the contour of thesheet is rectangular, and also the invention is applicable even to agroup of sheets in which sheets having various sizes are mixed.Furthermore, according to the present invention, since the opposite endsof one side edge are gripped, there is no need to hold the length of adiagonal of a rectangular sheet, but spreading of a sheet can beachieved automatically if a part of one side edge is initiallysupported, and therefore, the apparatus becomes compact andspace-saving. In addition, as the gripped corner of a sheet is grippedbya gripper after having been stretched and spreaded, the inconveniencethat folds, creases, twists and the like may be generated, is notpresent.

Although in a laundry factory, spreading of sheets (linens) and sortingworks for sheets relied upon human labor in the prior art, according tothe present invention, a worker need not untangle the whole of a sheet,but if he spreads out only a part of one edge and makes it gripped by agripper, the sheet can be automatically spreaded, and therefore, theworker can be released from a work under a hygienically bad environment,and energy saving at a laundry factory can be achieved.

While a principle of the present invention has been described above inconnection to preferred embodiments of the invention, it is intendedthat all matter contained in the specification and illustrated in theaccompanying drawings shall be interpreted to be illustrative and not asalimitation to the scope of the invention.

What is claimed is:
 1. A method of spreading a rectangular sheet, saidmethod comprising the steps of:gripping the rectangular sheet at atleast first and second points, the first of which points is locatedadjacent a first corner of the rectangular sheet so as to also beadjacent first and second side edges of the sheet intersecting at saidfirst corner and the second of which points is spaced from said firstcorner and is located adjacent said first side edge of the sheet, whileorienting that portion of the first side edge extending adjacent the atleast first and second points substantially horizontally in the air soas to suspend the sheet in a manner in which said second side edge ofthe sheet hangs substantially vertically from said first corner;subsequently gripping the sheet at a third point adjacent a secondcorner thereof located at the lowermost end of said second side edge ofthe sheet and at a fourth point adjacent said first corner and adjacentsaid second edge at the uppermost end thereof; and thereafter releasingthe sheet at least at said first and second points while holding saidsheet at said third and fourth points.